1. Field of the Invention
The present invention is directed to a method of determining complex pulse response of a radio channel, for instance the pulse response of radio channels of a digital mobile radio network (GSM network).
2. Description of the Prior Art
In radio networks in which radio signals are transmitted from one or several transmitters to a receiver, multipath propagation will result in interferences which may be expressed by the so-called complex pulse response of the radio channel. In digital mobile radio networks such as the so-called GSM radio networks such interferences due to multipath propagation appear as so-called inter-symbol interferences. When the pulse response of the radio channel is of longer duration than the duration of the bits transmitted via the radio channel, signal components of the received signal which form part of a symbol suffer from interference by components of previously transmitted symbols.
It has been known for measuring the complex pulse response to feed a special test signal by way of a specific standard signal generator into the radio channel to be measured and to determine the pulse response of the radio channel through the received signal as measured at the receiver by correlation with the transmitted test signal. This is disclosed in the following prior art references:
(S. Hermann, U. Martin, R. Reng, H. W. Schu.beta.ler, K. Schwarz: "Ein System for Ausbreitungsmessungen in Mobilfunkkanalen-Grundlagen und Realisierung", Kleinheubacher Berichte No. 34 (1991), pp. 615-624; PA1 G. Kadel, R. W. Lorenz: "Breitbandige Ausbreitungsmessungen zur Charakterisierung des Funkkanals beim GSM-System", Frequenz No. 45 (1991) pp. 158-163; PA1 W. Plagge, D. Poppen: "Neues Verfahren zur Messung der Kanalsto.beta.antwort und Tragersynchronisation in digitalen Mobilfunkkanalen", Frequenz 44 (1990) pp. 217-221; and PA1 J.-P. de Weck, J. Ruprecht: "Real-Time ML Estimation of Very Frequency-Selective Multipath Channels", IEEE Global Telecommunications Conference GLOBECOM'90, (December 1990).
The known measuring method requires a special standard signal generator at the transmitter end and is operative on condition that an unused radio channel is available. Therefore the known method is relatively expensive.